Heat recovery using fluidized spray tower

ABSTRACT

A fluidized spray vessel. A vessel design is provided for recovering heat from gaseous heat streams. The vessel utilizes a semi-fluidized bed for obtaining desirable liquid/vapor contact times. A spray section is provided in which liquid is sprayed through nozzles designed to provide a mean droplet size having a terminal velocity of from about sixty percent to about ninety five percent of the superficial upward gas velocity. These spray tower design criteria enhance spray tower performance, and thus enables more efficient heat recovery to be practiced, particularly in systems where relatively low grade heat sources are encountered.

RELATED APPLICATIONS

This patent application is a divisional of U.S. Application Ser. No.10/198,288 filed Jul. 17, 2002, entitled “FLUIDIZED SPRAY TOWER”, whichapplication claimed priority under 35 U.S.C. §119(e) from U.SApplication Ser. No. 60/306,401 filed on Jul. 17, 2001, entitled“FLUIDIZED SPRAY TOWER”, the disclosure of each of which is incorporatedherein in their entirety by this reference.

COPYRIGHT RIGHTS IN THE DRAWING

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The inventor has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, but otherwise reserves all copyright rightswhatsoever.

TECHNICAL FIELD

This invention relates to recovery of heat from hot gas streams, and,where appropriate, to the recovery of heat from moderate temperaturecombustion gas sources, such as boilers and incinerators. Morespecifically, the invention is directed to novel structures and methodsfor recovery of heat by direct contact of water with a hot gas stream.

BACKGROUND

Although various methods and structures have been provided for recoveryof waste heat, in so far as is known to me, conventional counter-currentspray towers heretofore have not provided for more than one transferunit for either mass or energy transfer systems. In part, this isbecause in such conventional spray tower designs, droplets fall througha rising gas in which the gas superficial velocity is at only a fractionof the terminal velocity of entering droplets.

In contact devices, it is important to observe that as the averagedroplet diameter decreases, the total surface area for the liquidincreases (area is proportional to 1 divided by the diameter of theaverage droplet). Also, an average contact period (dwell time) for adroplet entering a contact chamber depends on the terminal velocity ofthe droplet, its trajectory, and the path distance, as well as upon thevelocity of the gas encountered.

Unfortunately, conventional spray tower design has not matched nozzledesign developments. For the most part, conventional spray tower designshave ignored the use of any droplet diameter component, as a consequenceof using design methods such as the Souder-Brown equation, in which nodroplet diameter component appears. Thus, it would be desirable toprovide an improved spray tower that utilizes improved spray nozzletechnology to develop a narrow range of liquid droplet particle size.Also, it would be desirable to enhance spray tower performance byproviding spray nozzles that maximize droplet surface area. Finally, itwould be desirable to provide a spray tower in which dwell time isoptimized, so as to optimize heat transfer between the droplet and thegas stream through which it flows.

SUMMARY

A novel semi-fluidized spray tower design has been developed, and isdisclosed herein. The spray tower has been selected with spray nozzleswith a predetermined mean droplet size and surface area. Increaseddroplet dwell time in the countercurrent gas stream is provided,compared to conventional spray tower design criteria. In one embodiment,a spray tower built according to this new method has three distinctsections, including, from bottom to top, (1) a fluidization section, (2)a semi-fluidization spray section, and (3) a coalescing section.

In one embodiment, such an innovative spray tower is provided in asingle chamber design.

In yet another embodiment, the spray tower is provided in a two chamberdesign.

In various embodiments, the spray tower is provided in an open system,where water to be heated directly contacts the hot gas stream.

In other embodiments, the spray tower is provided in a closed system,where water to be heated does not directly contact the hot gas stream.

Various embodiments of the invention are disclosed in which themechanical or functional features described herein are achieved indisparate physical configurations.

BRIEF DESCRIPTION OF THE DRAWING

In order to enable the reader to attain a more complete appreciation ofthe invention, and of the novel features and the advantages thereof,attention is directed to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a generalized system schematic that shows a processgenerating waste heat, a conduit for taking a hot gas stream containingthe waste heat to the spray tower, and the innovative spray tower designprovided herein.

FIG. 2 provides a detailed view of a dual chamber fluidized spray vesseldesign.

FIG. 3 provides a vertical schematic of a dual chamber fluidized spraytower, indicating certain key dimensional data.

FIG. 4 provides a vertical schematic of a single chamber fluidized spraytower, indicating certain key dimensional data.

FIG. 5A provides a key to understanding the configurations illustratedin FIGS. 5B, 5C, 5D, and 5E.

FIG. 5B shows a brief process diagram illustrating the use of a dualchamber, open or direct contact type system incorporating a fluidizedspray tower.

FIG. 5C shows a brief process diagram illustrating the use of a dualchamber, closed or indirect contact type system incorporating afluidized spray tower.

FIG. 5D shows a brief process diagram illustrating the use of a singlechamber, open or direct contact type system incorporating a fluidizedspray tower.

FIG. 5E shows a brief process diagram illustrating the use of singlechamber, closed or indirect contact type system incorporating afluidized spray tower.

In the various figures, a prime mark (′) has been utilized to denotesimilar features or structures amongst the various embodiments, whereappropriate, without further mention thereof. In such cases, the readeris referred to the discussion of the feature or structure with respectto other embodiments where similar features or structures were earlierintroduced or explained, and a prime mark was not utilized in thereferenced figure.

The foregoing figures, being exemplary, contain various elements thatmay be present or omitted from actual implementations depending upon thecircumstances. An attempt has been made to draw the figures in a waythat illustrates at least those elements that are significant for anunderstanding of the various embodiments and aspects of the invention.However, various other elements of the exemplary spray tower and amethod of using the same to recover waste heat are also shown andbriefly described to enable the reader to understand how variousoptional features may be utilized, in order to provide an efficient,reliable, semi-fluidized bed spray tower system.

DETAILED DESCRIPTION

In FIG. 1, an overall system configuration is depicted for a typicalapplication for an innovative fluidized spray tower. FIGS. 1 and 2depict the operation of a basic, two chamber type open spray towerdesign. In an open type design, there is direct contact between the hotgas stream and the liquid medium, normally water, which is to be heated.

Process equipment 10 such as a boiler generates hot exhaust gas 12. Hotexhaust gas may also be advantageously provided from an engine, such asa gas turbine engine. Or, the hot exhaust gas may be provided from aprocess gas stream in an industrial process plant such as a paper mill.Such hot gas 12 may include as primary constituents, water vapor, carbondioxide, nitrogen, and a little oxygen, for example, in a typical boilerstack application. The hot gas 12 is provided to spray tower 20 througha hot gas conduit 22. Spray tower 20 structures may be fabricated usingconventional fabrication techniques in a vertically standingsubstantially tubular cylindrical shell design. However, otherconvenient shapes may be utilized, and any of such equivalent structuresmay be utilized according to the teachings herein in a method ofachieving heat recovery in a semi-fluidized direct contact heat transferapparatus.

As better seen in FIG. 2, the hot gas 12 enters the spray tower 20through a hot gas inlet 24, located in the lower portion 26 of the spraytower 20. The hot gas 12 is substantially prevented from downward escapeby a waste condensate pool 32. Waste condensate 35 travels to sewer 36through waste condensate drain 34.

After entry into spray tower vessel 20, the hot gas 12 gas enters thefluidization section 30 at the bottom portion of the spray tower 20. Inthe fluidization section 30 of tower 20, the upward gas velocity asrepresented by reference arrows 37 is designed for 200 percent or moreof the terminal velocity of the mean droplet size of the liquid medium(usually water) preselected for the spray nozzles in the device, asfurther described herein below. In this section, it is desirable toprevent the downward flow and escape of liquid droplets.

A liquid medium such as cold water stream 41 is provided through coldwater inlet 42. Water droplets 43 of a pre-determined mean droplet sizeare generated by one or more sets of spray nozzles 40 that are providedin fluid communication with water inlet 42. The cold water stream 41emerges through spray nozzles 40, which sprays droplets 43 downward,thus opposing the upflowing internal gas stream indicated by referencearrows G.

In the mid-tower semi-fluidized spray section 48, spray nozzles 40 (seeFIG. 3, for example) are oriented to distribute droplets evenly downwardover a cross-sectional area, in one embodiment, oriented perpendicularto the spray tower 20 vertical axis. Spray nozzles 40 are designed andprovided to develop a pre-determined mean droplet size having a terminalvelocity from about sixty (60) percent to about ninety five (95) percentof the local superficial upward gas velocity, the flow of which isindicated by reference arrows 50. Thus, in the upward flowing gasstream, the droplets fall relative to a fixed reference point along thevertical axis (indicated along centerline 52) at a rate from about five(5) percent to about forty (40) percent of their terminal velocity. Ofcourse, in any spray nozzle system, some droplets are generated in aspectrum of droplet sizes that includes droplets larger and smaller thanthe mean preselected size. However, very small droplets entrain in theupward flowing gas stream and leave the semi-fluidized section 48. Ifsuch droplets do not impinge on the containment vessel interior walls 54or other droplets 43, they are carried upward into the coalescingsection 56 above the spray nozzles 40. However, large droplets, andthose that become large droplets, fall, growing as they combine withother droplets, and eventually pass out of the semi-fluidized sectionand into the fluidized section. Other droplets 58 impinge on the towerwalls and then flow down into the contact water reservoir 74. Initially,substantially all small water droplets 43 of preselected size aresuspended at the top of the fluidized section 30, and do not fall downthrough the section until they agglomerate with other particles byincreasing their size (droplet 43′) and terminal velocity to ultimatelybecome larger particles 44, which particles fall downward into wastecondensate pool 32.

At the top of the tower, above spray from nozzle(s) 40, coalescingsection 56 is provided in which a coalescing device 68 acts as a targetto impinge and/or to intercept entrained droplets 67. The entraineddroplets 67 are thus mostly captured by coalescing into larger droplets,and then the larger droplets 69 fall back from the coalescing section 56into the semi-fluidized section 48.

A cooled gas stream 70 leaves the spray tower 20 at a cooled gas outlet72. The heat removed from the entering hot gas stream 12 is thuscaptured in contact water contained in the contact water reservoir 74,supported by reservoir bottom plate 76. In the embodiment shown in FIG.2, the reservoir bottom plate 76 is located intermediate the hot gasinlet 24 and the cooled gas outlet 72. A hot water stream 80 exits thereservoir 74 space outward via contact water reservoir outlet 82. Pump83 can be provided to recirculate the water exit stream 80 for reuse inthe semi-fluidized portion of spray tower 20, with makeup cold waterstream 41 provided as necessary.

With the operation of the basic two chamber type, open system spraytower 20 design having been described, as particularly set forth in FIG.2 and more generally in FIG. 5B, it is appropriate to describe alternateembodiments and additional structural details. First, with respect toFIG. 2, in the mid-portion 100 of tower 20, the contact water reservoirbottom plate 76 supports not only the contact water 101 captured, butalso provides support for, and is sealingly affixed to, an upwardoriented first gas passageway 102, tubular in nature, and in theembodiment shown in FIG. 2, a cylindrical tube that is located along thecenterline 52 of the spray tower 20. At the lower end 104 of first gaspassageway one or more baffle(s) 106 and endplate 108 provide for adesirable change in direction of entering gas, to help deflect droplets.At the upper end 110 of first gas passageway, one or more baffle(s) 112and endplate or hat portion 115 provide for deflection of downwardlyoriented spray of droplets, and provide a tortuous gas path havingdesirable change in direction for the upwardly direct gas 116 exitingthe first gas passageway 102.

At the upper portion 120 of the spray tower 20, a second gas passageway122 is provided. As shown in the embodiment depicted in FIG. 2, thesecond gas passageway 122 is also of a cylindrical tubular shape. At thelower end 123 of the second gas passageway 122, one or more baffle(s)124 are provided as well as end plate or target 126 (circular, asdepicted affixed to baffles 124), to assist in impinging and/orintercepting droplets, by providing a tortuous gas pathway through whichthe exiting gas must flow, in order to minimize droplets lost viaentrainment.

At the upper water level limit 150 of the reservoir 74 for contact wateror other liquid medium, a downwardly extending reservoir drain pipe 152is provided, extending from upper end 151 downward through bottom plate76 and on downward toward the lower portion 26 of the vessel 20, to alower end 153, in fluid communication with drain 34, and thus allowingcondensate 154 to join waste condensate 35 to drain out of vessel 20through the waste condensate drain 34.

In other embodiments, a closed process system design can be provided asindicate in FIGS. 5C and 5E. First, in FIG. 5C, water 80 leaving thecontact water reservoir 74 is sent to a pump 200, which provides motiveforce for sending the water through a heat exchanger 202. Heat exchanger202 is provided with a cold water supply stream 204, which cold watersupply stream is heated in the heat exchanger 202 to provide a hot,non-contact water stream 210 exiting the heat exchanger 202. The cooledcontact water stream 206 enters vessel as the inlet cold water stream atspray nozzles 220.

A single chamber embodiments is illustrated in FIGS. 5D and 5E. Like inthe case of a dual chamber design, the single chamber design can beprovided in either (1) a direct contact design, or (2) a closed system,non-contact design. Note that in the single chamber design depicted inthese figures, the bottom portion 30 as shown in vessel 20 of FIG. 2 isdispensed with, and the hot gas enters directly under baffling 300 andshortly encounters spray from nozzles 302 and/or 304. Note that both anoutside, cold water inlet stream 310 is provided, as well as a recyclestream 312, sent through pump 314, to further warm the process waterrecirculating in the unit. Pump 314 also serves as a hot contact processwater 316 outlet. Overflow is sent outward through internal reservoiroutlet or drain 152′ and is then sent to sewer 36 or other appropriateend use or disposal point. If the configuration is for a closed systemdesign, as set forth in FIG. 5E, then a heat exchanger system as earlierexplained in relation to FIG. 5C is utilized.

Turning now to FIG. 3, some exemplary dimensional data for one desirableembodiment of spray vessel 20′ are illustrated. As shown, the spraynozzles 40′ are located a distance S apart, vertically. From the upperrow of nozzles 40′₁ to the top of the vessel 20′, a distance 3.5 S isprovided. From the lower nozzle 40′₃ a distance of 2 S is provided abovethe outlet end 115 of the first gas passageway 102. Also, first gaspassageway 102 is shown in a 48 inch height, which may be desirable inmany cases, but that distance should be considered merely exemplary forthis one embodiment. Various other dimensions are detailed, including alower portion 30 (reference FIG. 2) dimension of 3.5 times the diameter“d” of the gas outlet 72. A sloping bottom sump 400 is provided in aheight of 0.5 times the overall vessel 20′ diameter D.

Similar dimensions are indicated in FIG. 4 for a single vessel chamberdesign of the type schematically illustrated in FIGS. 5D and 5E.

It is to be appreciated that the various aspects and embodiments of thefluidized spray tower designs described herein are an importantimprovement in the state of the art, especially for recovery of heatfrom low grade heat sources. Although only a few exemplary embodimentshave been described in detail, various details are sufficiently setforth in the drawings and in the specification provided herein to enableone of ordinary skill in the art to make and use the invention(s), whichneed not be further described by additional writing in this detaileddescription. Importantly, the aspects and embodiments described andclaimed herein may be modified from those shown without materiallydeparting from the novel teachings and advantages provided by thisinvention, and may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. Therefore, theembodiments presented herein are to be considered in all respects asillustrative and not restrictive. As such, this disclosure is intendedto cover the structures described herein and not only structuralequivalents thereof, but also equivalent structures. Numerousmodifications and variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, the invention(s) may be practiced otherwise than asspecifically described herein. Thus, the scope of the invention(s), asset forth in the appended claims, and as indicated by the drawing and bythe foregoing description, is intended to include variations from theembodiments provided which are nevertheless described by the broadinterpretation and range properly afforded to the plain meaning of theclaims set forth below.

1. An apparatus for recovering heat from a heat containing gaseousstream, by transfer of said heat into a liquid medium, said apparatuscomprising: (a) a containment vessel having an interior wall, saidvessel extending along a central axis and having (i) a hot gas inlet,(ii) a cooled gas outlet; (b) a liquid medium outlet, said liquid mediumoutlet adapted for removing liquid medium from said vessel; (c) a liquidmedium inlet, said liquid medium inlet located between said hot gasinlet of said vessel and said cooled gas outlet of said vessel; (d) influid communication with said liquid medium inlet, one or more spraynozzles, said spray nozzles adapted to spray said liquid medium downwardtoward said hot gas inlet; (e) a coalescer, said coalescer locatedadjacent said cooled gas outlet of said vessel, and adapted to coalesceliquid droplets attempting to escape outward through said hot gasoutlet.
 2. A method of recovering heat from a hot gas by transferringheat to a liquid medium, said method comprising: (a) providing a vesselas set forth in claim 1; (b) providing a semi-fluidized spray section insaid vessel, said spray section having downwardly directed spray nozzlesfor spraying a liquid medium into which heat is to be recovered fromsaid gas, said spray nozzles sized and shaped to develop a mean dropletsize having a terminal velocity from about sixty percent to about ninetyfive percent of the superficial upward gas velocity in saidsemi-fluidized bed section, such that said droplets fall relative to afixed reference point in said spray section from about five percent toabout forty percent of the terminal velocity of said droplets.
 3. Themethod as set forth in claim 2, further comprising (1) an external heatexchanger, and (2) an intermediate heating medium, wherein said hot gasheats said intermediate heating medium, and wherein a liquid streamwhich does not directly contact said hot gas is heated.